So the way I understand it the Undaunted Event starts tomorrow at 10.00am EST which is 3.00pm for Europe and runs on a 20 hour reset for the dungeons !
That means not being able to start a dungeon early say at 6.00am like the writs, until the days have worked round by which it will be almost ended.
I can imagine the dungeon queues will be chocablock with lots of players trying to queue.
Someone correct me if I am wrong (hopefully I am) about the amount of hours to reset. I only picked this up because of a tweet from ESO reminding players about the reset !
PC - EU